- Converting Between Numbers and Strings
- Converting Numbers to Strings
- Вопрос-ответ: как в Java правильно конвертировать String в int?
- Обсуждение
- String to Int in Java – How to Convert a String to an Integer
- How to Convert a String to an Integer in Java Using Integer.parseInt
- How to Convert a String to an Integer in Java Using Integer.valueOf
- Summary
- String to Int in Java – How to Convert a String to an Integer
- How to Convert a String to an Integer in Java Using Integer.parseInt
- How to Convert a String to an Integer in Java Using Integer.valueOf
- Summary
- Java String to Int – How to Convert a String to an Integer
- 1. Use Integer.parseInt() to Convert a String to an Integer
- 2. Use Integer.valueOf() to Convert a String to an Integer
Converting Between Numbers and Strings
Frequently, a program ends up with numeric data in a string objecta value entered by the user, for example.
The Number subclasses that wrap primitive numeric types ( Byte , Integer , Double , Float , Long , and Short ) each provide a class method named valueOf that converts a string to an object of that type. Here is an example, ValueOfDemo , that gets two strings from the command line, converts them to numbers, and performs arithmetic operations on the values:
public class ValueOfDemo < public static void main(String[] args) < // this program requires two // arguments on the command line if (args.length == 2) < // convert strings to numbers float a = (Float.valueOf(args[0])).floatValue(); float b = (Float.valueOf(args[1])).floatValue(); // do some arithmetic System.out.println("a + b = " + (a + b)); System.out.println("a - b = " + (a - b)); System.out.println("a * b = " + (a * b)); System.out.println("a / b = " + (a / b)); System.out.println("a % b = " + (a % b)); >else < System.out.println("This program " + "requires two command-line arguments."); >> > The following is the output from the program when you use 4.5 and 87.2 for the command-line arguments:
a + b = 91.7 a - b = -82.7 a * b = 392.4 a / b = 0.0516055 a % b = 4.5
Note: Each of the Number subclasses that wrap primitive numeric types also provides a parseXXXX() method (for example, parseFloat() ) that can be used to convert strings to primitive numbers. Since a primitive type is returned instead of an object, the parseFloat() method is more direct than the valueOf() method. For example, in the ValueOfDemo program, we could use:
float a = Float.parseFloat(args[0]); float b = Float.parseFloat(args[1]);
Converting Numbers to Strings
Sometimes you need to convert a number to a string because you need to operate on the value in its string form. There are several easy ways to convert a number to a string:
int i; // Concatenate "i" with an empty string; conversion is handled for you. String s1 = "" + i;
// The valueOf class method. String s2 = String.valueOf(i);
Each of the Number subclasses includes a class method, toString() , that will convert its primitive type to a string. For example:
int i; double d; String s3 = Integer.toString(i); String s4 = Double.toString(d);
The ToStringDemo example uses the toString method to convert a number to a string. The program then uses some string methods to compute the number of digits before and after the decimal point:
public class ToStringDemo < public static void main(String[] args) < double d = 858.48; String s = Double.toString(d); int dot = s.indexOf('.'); System.out.println(dot + " digits " + "before decimal point."); System.out.println( (s.length() - dot - 1) + " digits after decimal point."); >> The output of this program is:
3 digits before decimal point. 2 digits after decimal point.
Вопрос-ответ: как в Java правильно конвертировать String в int?
int в String — очень просто, и вообще практически любой примитивный тип приводится к String без проблем.
int x = 5; String text = "X lang-java line-numbers">int i = Integer.parseInt (myString); Если строка, обозначенная переменной myString , является допустимым целым числом, например «1», «200», Java спокойно преобразует её в примитивный тип данных int . Если по какой-либо причине это не удается, подобное действие может вызвать исключение NumberFormatException , поэтому чтобы программа работала корректно для любой строки, нам нужно немного больше кода. Программа, которая демонстрирует метод преобразования Java String в int , управление для возможного NumberFormatException :
public class JavaStringToIntExample < public static void main (String[] args) < // String s = "fred"; // используйте это, если вам нужно протестировать //исключение ниже String s = "100"; try < // именно здесь String преобразуется в int int i = Integer.parseInt(s.trim()); // выведем на экран значение после конвертации System.out.println("int i = " + i); >catch (NumberFormatException nfe) < System.out.println("NumberFormatException: " + nfe.getMessage()); >> Обсуждение
Когда вы изучите пример выше, вы увидите, что метод Integer.parseInt (s.trim ()) используется для превращения строки s в целое число i , и происходит это в следующей строке кода:
int i = Integer.parseInt (s.trim ())- Integer.toString (int i) используется для преобразования int в строки Java.
- Если вы хотите преобразовать объект String в объект Integer (а не примитивный класс int ), используйте метод valueOf () для класса Integer вместо метода parseInt () .
- Если вам нужно преобразовать строки в дополнительные примитивные поля Java, используйте такие методы, как Long.parseLong () и ему подобные.
String to Int in Java – How to Convert a String to an Integer
Ihechikara Vincent Abba
When working with a programming language, you may want to convert strings to integers. An example would be performing a mathematical operation using the value of a string variable.
In this article, you'll learn how to convert a string to an integer in Java using two methods of the Integer class — parseInt() and valueOf() .
How to Convert a String to an Integer in Java Using Integer.parseInt
The parseInt() method takes the string to be converted to an integer as a parameter. That is:
Integer.parseInt(string_varaible)Before looking at an example of its usage, let's see what happens when you add a string value and an integer without any sort of conversion:
In the code above, we created an age variable with a string value of "10".
When added to an integer value of 20, we got 1020 instead of 30.
Here's a quick fix using the parseInt() method:
In order to convert the age variable to an integer, we passed it as a parameter to the parseInt() method — Integer.parseInt(age) — and stored it in a variable called age_to_int .
When added to another integer, we got a proper addition: age_to_int + 20 .
How to Convert a String to an Integer in Java Using Integer.valueOf
The valueOf() methods works just like the parseInt() method. It takes the string to be converted to an integer as its parameter.
The explanation for the code above is the same as the last section:
- We passed the string as a parameter to valueOf() : Integer.valueOf(age) . It was stored in a variable called age_to_int .
- We then added 20 to the variable created: age_to_int + 20 . The resulting value was 30 instead of 1020.
Summary
In this article, we talked about converting strings to integers in Java.
We saw how to convert a string to an integer in Java using two methods of the Integer class — parseInt() and valueOf() .
String to Int in Java – How to Convert a String to an Integer
Ihechikara Vincent Abba
When working with a programming language, you may want to convert strings to integers. An example would be performing a mathematical operation using the value of a string variable.
In this article, you'll learn how to convert a string to an integer in Java using two methods of the Integer class — parseInt() and valueOf() .
How to Convert a String to an Integer in Java Using Integer.parseInt
The parseInt() method takes the string to be converted to an integer as a parameter. That is:
Integer.parseInt(string_varaible)Before looking at an example of its usage, let's see what happens when you add a string value and an integer without any sort of conversion:
In the code above, we created an age variable with a string value of "10".
When added to an integer value of 20, we got 1020 instead of 30.
Here's a quick fix using the parseInt() method:
In order to convert the age variable to an integer, we passed it as a parameter to the parseInt() method — Integer.parseInt(age) — and stored it in a variable called age_to_int .
When added to another integer, we got a proper addition: age_to_int + 20 .
How to Convert a String to an Integer in Java Using Integer.valueOf
The valueOf() methods works just like the parseInt() method. It takes the string to be converted to an integer as its parameter.
The explanation for the code above is the same as the last section:
- We passed the string as a parameter to valueOf() : Integer.valueOf(age) . It was stored in a variable called age_to_int .
- We then added 20 to the variable created: age_to_int + 20 . The resulting value was 30 instead of 1020.
Summary
In this article, we talked about converting strings to integers in Java.
We saw how to convert a string to an integer in Java using two methods of the Integer class — parseInt() and valueOf() .
Java String to Int – How to Convert a String to an Integer
Thanoshan MV
String objects are represented as a string of characters.
If you have worked in Java Swing, it has components such as JTextField and JTextArea which we use to get our input from the GUI. It takes our input as a string.
If we want to make a simple calculator using Swing, we need to figure out how to convert a string to an integer. This leads us to the question – how can we convert a string to an integer?
In Java, we can use Integer.valueOf() and Integer.parseInt() to convert a string to an integer.
1. Use Integer.parseInt() to Convert a String to an Integer
This method returns the string as a primitive type int. If the string does not contain a valid integer then it will throw a NumberFormatException.
So, every time we convert a string to an int, we need to take care of this exception by placing the code inside the try-catch block.
Let's consider an example of converting a string to an int using Integer.parseInt() :
String str = "25"; try < int number = Integer.parseInt(str); System.out.println(number); // output = 25 >catch (NumberFormatException ex)
Let's try to break this code by inputting an invalid integer:
String str = "25T"; try < int number = Integer.parseInt(str); System.out.println(number); >catch (NumberFormatException ex)
As you can see in the above code, we have tried to convert 25T to an integer. This is not a valid input. Therefore, it must throw a NumberFormatException.
Here's the output of the above code:
java.lang.NumberFormatException: For input string: "25T" at java.lang.NumberFormatException.forInputString(NumberFormatException.java:65) at java.lang.Integer.parseInt(Integer.java:580) at java.lang.Integer.parseInt(Integer.java:615) at OOP.StringTest.main(StringTest.java:51)Next, we will consider how to convert a string to an integer using the Integer.valueOf() method.
2. Use Integer.valueOf() to Convert a String to an Integer
This method returns the string as an integer object. If you look at the Java documentation, Integer.valueOf() returns an integer object which is equivalent to a new Integer(Integer.parseInt(s)) .
We will place our code inside the try-catch block when using this method. Let us consider an example using the Integer.valueOf() method:
String str = "25"; try < Integer number = Integer.valueOf(str); System.out.println(number); // output = 25 >catch (NumberFormatException ex)
Now, let's try to break the above code by inputting an invalid integer number:
String str = "25TA"; try < Integer number = Integer.valueOf(str); System.out.println(number); >catch (NumberFormatException ex)
Similar to the previous example, the above code will throw an exception.
Here's the output of the above code:
java.lang.NumberFormatException: For input string: "25TA" at java.lang.NumberFormatException.forInputString(NumberFormatException.java:65) at java.lang.Integer.parseInt(Integer.java:580) at java.lang.Integer.valueOf(Integer.java:766) at OOP.StringTest.main(StringTest.java:42)We can also create a method to check if the passed-in string is numeric or not before using the above mentioned methods.
I have created a simple method for checking whether the passed-in string is numeric or not.
public class StringTest < public static void main(String[] args) < String str = "25"; String str1 = "25.06"; System.out.println(isNumeric(str)); System.out.println(isNumeric(str1)); >private static boolean isNumeric(String str) < return str != null && str.matches("[0-9.]+"); >>The isNumeric() method takes a string as an argument. First it checks if it is null or not. After that we use the matches() method to check if it contains digits 0 to 9 and a period character.
This is a simple way to check numeric values. You can write or search Google for more advanced regular expressions to capture numerics depending on your use case.
It is a best practice to check if the passed-in string is numeric or not before trying to convert it to integer.
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Happy Coding!